Consumption of poultry products contaminated with Salmonella bacteria is a significant source of gastrointestinal infections in humans. For example, Salmonella enteritidis, especially phage type 4, has become more common in both poultry and humans since the early 1980's. The prevalence of Salmonella typhimurium, on the other hand, has remained relatively stable. However, the spread of the antibiotic-resistant strain DT104 in domestic flocks gives some reason for concern. Accordingly, the presence of Salmonella in commercial meat and food products is a major public health concern given that such infections can lead to serious illness or, in severe cases, death. Further, Salmonella infections in chickens, turkeys and ducks raise concerns for poultry producers due to increasing rates of morbidity and mortality as well as losses attributable culling and/or rejection of infected birds.
Salmonella infections can be spread via intraspecies or horizontal transmission, i.e., from animal to animal, and/or via interspecies or vertical transmission, i.e., from animal to humans. Generally, horizontal transmission of Salmonella bacteria is typically via exposure to environmental factors such as, for example, contaminated feces, bedding, nesting materials and/or other fomites. In contrast, vertical transmission of Salmonella bacteria is typically via oral exposure to the bacteria such by handling contaminated raw meats. Vertical transmission can also occur via shell contamination and/or internal transovarian contamination of the yolk of eggs produced by infected birds.
The basis for good control of Salmonella infections in farm environments, in particular, in poultry farms, is good farming and hygiene practices. Such practices include, for example, managing and preventing contamination of feeds, monitoring of animal health, cleaning and disinfection of coops and pens, and control of pest species such as, for examples, rodents. Testing and removal of infected or pathogen-positive animals from production and/or contact with uninfected animals are also vital to controlling horizontal and/or vertical transmission of such infections.
Poultry infected with Salmonella bacteria generally develop a strong immune response to the pathogen which is typically manifested by progressive reduction in excretion of the organism and reduced disease and excretion upon subsequent challenge. Accordingly, there is a need for an effective means for inducing an immune response to Salmonella bacteria in poultry which results in reduced disease and excretion or shedding of the bacteria while reducing productivity losses attributable to culling and/or rejection of infected birds.
Recently, vaccination of commercial poultry flocks to increase resistance against pathogenic exposure to Salmonella has become more prevalent particularly in view of increasing public awareness. However, such vaccination programs are generally difficult, time consuming and/or prohibitively expensive to administer on a commercial production scale. Accordingly, there is a need for an effective means for vaccinating domestic poultry and fowl against Salmonella infections.
Additionally, it is generally believed that vaccination is not a control option for serovars other than Salmonella enteritidis and Salmonella typhimurium which can be present on poultry farms. It is also generally believed that vaccination has limited effect on improving animal health and welfare and such vaccines are primarily used for public health reasons. Accordingly, there is a need for an antigen composition or vaccine effective to result in improved avian health and welfare such as can be manifested by increased weight gain and reduced mortality.
Further, some antigens may interfere with efficacy of other vaccines or medications administered simultaneously with and/or subsequent to vaccination. Additionally or alternatively, particular antigens may interfere with or affect the accuracy of traditional test or screening tools used to detect active or prior infection. Accordingly, there is a demand for a Salmonella antigen which can be administered to domestic poultry and fowl which does not reduce the effectiveness of other vaccines such as, for example, Marek's disease vaccines.